Radio Frequency IDentification (RFID) systems include RFID readers and RFID tags. The tags can be used in many ways for locating and identifying objects that they are attached to. RFID tags are particularly useful in product-related and service-related industries for tracking large numbers of objects are being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to individual items, or to their packages.
In principle, RFID techniques entail using an RFID reader to interrogate one or more RFID tags. Interrogation is performed by the reader transmitting a Radio Frequency (RF) wave. A tag that senses the interrogating RF wave responds by transmitting back another RF wave, a process known as backscatter. Backscatter may take place in a number of ways. The response may further encode a number stored internally in the tag. The response, and the number if available, is decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The number can denote a serial number, a price, a date, a destination, other attribute(s), any combination of attributes, and so on.
An RFID tag typically includes an antenna system, a power management section, a radio section, a logical section, and a memory. Advances in semiconductor technology have miniaturized the electronics so much that an RFID tag can generate the backscatter while powered by only the RF signal it receives, enabling some RFID tags to operate without a battery.
A challenge in the operation of RFID systems arises when a tag or population of tags does not know how to communicate with a reader. A number of communication parameters may be at issue, for example the reader's transmission data rate, a ratio of duration of the different symbols, the expected backscatter rate, and so on.
Another challenge in the operation of RFID systems arises from interference, when other RF signals are also transmitted in the vicinity at the same time. Interfering RF signals may be generated, for example, from nearby wireless devices such as other RFID readers, and also cordless telephones, wireless baby monitors, and the like. In those instances, an RFID tag cannot detect the interrogating RF wave reliably, or parse its commands.